US planemaker Boeing said on Friday that Xiamen Airlines, a unit of China Southern Airlines, had agreed to purchase 40 next-generation 737-800s -- an order valued at $3.5 billion at list prices.
The deal requires Chinese regulatory approval, Boeing said in a statement, adding that it would work with Xiamen Airlines to push through the deal.
Boeing said the airline planned to use the new aircraft for "more international routes to meet growing passenger traffic in Asia-Pacific and China."
Xiamen Airlines, which is due to join the Skyteam alliance by the end of the year, operates an all-Boeing fleet of six 757s and 77 next-generation 737s.
"The carrier plans to grow its operational fleet to 200 airplanes by the end of year 2020," Boeing said.
Demand for air traffic in China has boomed as the country's economy roars ahead and an increasingly affluent middle class travels more frequently.
China Southern Airlines, one of China's big three carriers along with Air China and China Eastern Airlines, owns 60 percent of Xiamen Airlines.
On Friday, SilkAir, the regional wing of Singapore Airlines (SIA), said it would buy 54 new Boeing planes in a deal worth $4.9 billion, with an option to buy a further 14 aircraft.
SilkAir said the firm orders will cover 23 737-800s and 31 737 MAX 8s, in a deal worth $4.9 billion based on Boeing's current list prices.
The orders will help Boeing bridge the gap with European rival Airbus.
The B737-800 is the best selling variant of Boeing's popular next-generation family of single-aisle aircraft. It can carry up to 189 passengers. The 737 MAX is currently in development.